When sticking a pressure-sensitive adhesive sheet onto an adherend by hand, entrapment of air between the adherend and the pressure-sensitive adhesive surface may occur, marring the appearance of the pressure-sensitive adhesive sheet. Such air entrapment is particularly prone to occur in the case that the pressure-sensitive adhesive sheet has a large area.
To eliminate problems with appearance of a pressure-sensitive adhesive sheet due to air entrapment, another pressure-sensitive adhesive sheet may be stuck on in place of the preceded pressure-sensitive adhesive sheet, or the attached pressure-sensitive adhesive sheet may be peeled off and then reattached, or a hole may be made with a needle in a blistered portion of the pressure-sensitive adhesive sheet so as to allow the air to escape. However, in the case of sticking on in place of pressure-sensitive adhesive sheet, effort is required, and furthermore the cost is increased; moreover, in the case of reattaching the original pressure-sensitive adhesive sheet, problems often arise such as the pressure-sensitive adhesive sheet tearing, or wrinkles forming on the surface, or the adhesiveness dropping. On the other hand, the method of making a hole with a needle mars the appearance of the pressure-sensitive adhesive sheet.
To prevent air entrapment from occurring, there is a method in which water is put onto the adherend or the pressure-sensitive adhesive surface in advance before the two are stuck together; however, in the case of sticking on a pressure-sensitive adhesive sheet having large dimensions such as a safety film stuck onto a window, a decorative film or a marking film, much time and effort is required. Moreover, there is a method in which air entrapment is prevented from occurring by sticking on the pressure-sensitive adhesive sheet using a device rather than by hand; however, depending on the use of the pressure-sensitive adhesive sheet or the site or shape of the adherend, it may not be possible to use such a device for sticking on the pressure-sensitive adhesive sheet.
Meanwhile, a resin material such as an acrylic resin, an ABS resin, a polystyrene resin or a polycarbonate resin may emit a gas upon heating or even with no heating; in the case of sticking a pressure-sensitive adhesive sheet onto an adherend made of such a resin material, blistering may occur on the pressure-sensitive adhesive sheet due to the gas emitted from the adherend.
Moreover, in the case of sticking a pressure-sensitive adhesive sheet onto an adherend made of a resin through which gas readily permeates, gas that has permeated through may build up between the adherend and the pressure-sensitive adhesive sheet, so that the pressure-sensitive adhesive sheet blisters or peels off. For example, in the case that a marking sheet is stuck onto a motorbike gasoline tank made of polyethylene resin, vapor of gasoline in the gasoline tank may vaporize so as to permeate through the polyethylene resin layer of the gasoline tank, so that the marking sheet blisters or peels off, bringing about an undesirable situation such as the appearance being marred.
To solve such problems, with a pressure-sensitive adhesive sheet described in Japanese Patent Application Laid-open No. H2-107682, a substrate and a pressure-sensitive adhesive layer are subjected to punching processing using a blade die and a hole die so as to form through-holes of diameter from 0.2 to 1.0 mm therein, and with a pressure-sensitive adhesive sheet described in Japanese Utility Model Application Laid-open No. H4-100235, a substrate and a pressure-sensitive adhesive layer are subjected to perforation processing using a hot needle so as to form through-holes of diameter from 0.05 to 0.15 mm therein; air or gas escapes from these through-holes to the outside, whereby air entrapment and blistering of the pressure-sensitive adhesive sheet are prevented.
However, with the above pressure-sensitive adhesive sheets, the through-holes can be seen with the naked eye, and hence the appearance of the pressure-sensitive adhesive sheet is not necessarily good. In particular, in the case of forming the through-holes using a hot needle as with the pressure-sensitive adhesive sheet described in Japanese Utility Model Application Laid-open No. H4-100235, portions where the substrate melts and thus rises up mar the appearance of the pressure-sensitive adhesive sheet.
Moreover, with the above pressure-sensitive adhesive sheets, there has been a problem that if liquid such as water or gasoline becomes attached to the pressure-sensitive adhesive sheet after the pressure-sensitive adhesive sheet has been stuck onto an adherend, then this liquid enters into the through-holes, causing the through-hole portions (portions around the peripheries of the through-holes) to swell or the like so that the appearance of the pressure-sensitive adhesive sheet is marred.
The present invention has been devised in view of the above state of affairs; it is an object of the present invention to provide a pressure-sensitive adhesive sheet according to which air entrapment and blistering can be prevented or eliminated via through-holes, and yet the appearance compares favorably with that of a pressure-sensitive adhesive sheet having no through-holes therein.